Wet processing of many types of objects often includes a step of separating the object from the liquid as either a finished product or for further processing. Moreover, it is often desirable to rinse and/or clean the object after wet processing to remove any contaminants or left over and unwanted processing liquids and to provide a clean processed object. Also, in many cases, depending on any further treatment or handling, the object may be further dried to remove any processing or rinsing liquids that may still be present on a surface of the object.
In the case of processing microelectronic devices, such as including semiconductor wafers at any of various stages of processing, flat panel displays, microelectrical-mechanical-systems (MEMS), advanced electrical interconnect systems, optical components and devices and components of mass data storage devices (disk drives) and the like, cleanliness is critical in virtually all processing aspects. Representative steps in wet processing of wafers include wafer etching and rinsing. For processing such microelectronic devices, it is important to use clean processing liquids so as not to introduce contaminants into the processing environment, and likewise as important to separate the wafer(s) from the liquid bath in a way to substantially prevent contaminant deposition onto a wafer surface, including contaminants that may be suspended within the liquid bath (as potentially present from the processing liquid, the wafer surface, or as a result of the processing step).
In this regard, techniques and apparatuses have been developed for rinsing and separating wafers from immersion (or liquid bath) type processes, and, by such process or by a subsequent drying process, to leave wafer surfaces substantially clean. A popular rinsing technique is known as cascade rinsing. Such cascade rinsing utilizes a cascade rinser having inner and outer chambers that are separated from one another by a partition or weir. Rinse water flows from a water source into the inner chamber. The inner chamber fills with rinsing liquid until it overflows so that rinsing liquid cascades over the partition or weir into the outer chamber. Typically, DI water is used as the rinsing liquid, which DI water is preferably rendered extremely clean, such as by filtering as disclosed in U.S. Pat. Nos. 5,542,441, 5,651,379 and 6,312,597 to Mohindra et al.
Separation, itself, can be accomplished in many different ways utilizing many different kinds and complexities of mechanisms. However, the basic step of separation is relatively quite simply characterized as the gradual replacement of a liquid environment about an object or portion thereof with a gas environment. For an inline type immersion process, separation is typically done by replacing one fluid that is supplied inline with a subsequent fluid (e.g. changing from rinse liquid to clean gas). See, for example, U.S. Pat. Nos. 4,984,597 and 4,911,761 to McConnell et al. For a liquid bath type immersion process (i.e. where one or more wafers are supported or suspended within liquid contained by a vessel), such separation is normally accomplished by either lifting the wafers from the bath or by draining the liquid from the vessel. For lifting, many different wafer handlers or elevators are known for lifting wafers themselves or for lifting a wafer cassette or the like that may support and contain many wafers as a set. Where the liquid bath is drained, the wafers may be supported by structure within the vessel or by a removable cassette so that the wafers can be stationary during liquid removal.
Separation itself, however, does not necessarily result in dry wafers. That is, after a rinsing step, a drying step may need to be conducted depending on parameters of the separation (e.g. speed of separation, orientation of the wafers, and the like) as well as characteristics of the wafers themselves (e.g. hydrophilic or hydrophobic nature of the wafer surface). Any liquid droplets or films that remain on a wafer surface after separation, such as may result at or near contact points with support structure or as minute droplets or films that hold to the wafer surface, are desirably removed from the wafer surface. If such droplets or films are left to evaporate from the wafer surface, any contaminants within the droplets or films will be deposited on the wafer surface, which contaminants may render a portion of the wafer unsuitable for further processing or use. Known drying techniques include the use of heated liquids and/or heated gases, such as heated nitrogen gas, during and after the rinsing step for removing unwanted droplets and films from the wafer surfaces. However, minute liquid droplets or films are sometimes very difficult to remove due to their attraction to the wafer surfaces.
A manner to enhance rinsing and separation of the wafers from the liquid bath so that liquid droplets and films do not substantially remain on the wafer surfaces after separation has been developed based on the introduction of a cleaning enhancement substance that tends to accelerate liquid from the wafer surface during separation by reducing surface tension of the liquid near the wafer surface. By cleaning enhancement, it is meant that the separation step is enhanced or improved by the presence of the substance, i.e. a cleaner separation results. Specifically, it is known to use isopropyl alcohol (IPA) that is supplied within a gas environment that replaces the liquid environment. Whether the process is an in-line process, a liquid drain process or a wafer lift process, the liquid environment surrounding the wafers is replaced by a gas environment, which gas environment can comprise the IPA with other gas and/or a carrier gas. As an example of an in-line process, U.S. Pat. No. 4,911,761 to McConnell et al. describes the use of superheated saturated drying vapor as a drying fluid that is used to replace a liquid environment. Processes and techniques for replacing the liquid environment surrounding wafers with a gas environment that includes a cleaning enhancement substance such as IPA in dilute quantity for effectively cleaning wafer surfaces during the separation stage are described in U.S. Pat. No. 5,772,784 to Mohindra et al. The specific processes described within Mohindra et al. include draining rinse liquid from a vessel for separating the liquid from the wafer surfaces. Methods of separating wafers from a liquid rinse environment within a vessel by lifting the wafers while supplying IPA above the wafers are described in U.S. Pat. Nos. 6,012,472, 6,139,645 and 6,170,495 to Lenaars et al.
Methods utilizing dilute quantities of IPA are a significant improvement in that wafer may be successfully rinsed, cleaned and dried with lower chemical usage, which is more environmentally friendly as well as less costly. The same is desirable with any and all processing chemicals that may be utilized within an immersion vessel for processing wafers. As the above-noted prior art describes, batch processing of a set of wafers together is desired for wafer processing throughput as well as to use such processing chemicals most effectively. However, such chemical use effectiveness is based upon the processing of a full set of wafers at all times. Processing of less than a full set becomes less and less effective because the vessels themselves contain the same volumes that must be filled by processing liquids as well as processing gases, thereby increasing the volume of process fluids and gases used per wafer processed.